Defective influenza (DI) viruses interfere with the replication of infectious influenza viruses. We propose to study the mechanism of interference by DI influenza viruses. We hope to quantitate the complexity of influenza viral genome and determine the inter-relationship between viral RNA segments. We hope to determine the amount and location of the delection in DI viral genome. We hope to find out the nature of interfering molecule ie. viral RNA, complementary RNA or ribonucleoprotein. We hope to determine if the interference is at the level of transcription, replication or translation of viral genome or in the assembly and transport of viral proteins. Finally, we hope to determine if the interference induced by DI viruses is narrow (strain specific) or broader (non strain specific).